1. Field of the Invention
The invention relates to a weld detecting method and a weld detecting apparatus that detect a position of a weld on a work.
2. Description of the Related Art
When forming a work by joining two end portions of sheet-like portions together by welding, for example, a weld is formed on the work. In the work, the characteristics such as hardness and the like of the weld are different than they are at other portions. Therefore, it is necessary to detect the position of a weld in order to check just the weld or perform machining on portions other than the weld. However, when a worker detects, through visual confirmation, a weld on a work that has been elongated by rolling or the like, it is extremely difficult to discern the position of the weld, so detection takes more time. Examples of such a work include metal rings and metal bands.
Japanese Patent Application Publication No. 61-151455 (JP-A-61-151455) and Japanese Patent Application Publication No. 2005-283303 (JP-A-2005-283303), for example, describe weld detecting methods.
JP-A-61-151455 describes detecting a weld on a work after rolling. In JP-A-61-151455, a movable detection sensor is used to detect a weld on a work after rolling. The detection sensor generates an eddy current inside the work and detects a weld by detecting this eddy current with a detecting portion. Also, a detection signal detected by the detecting portion is filtered by a filtering portion. This kind of detection sensor is moved around to detect the weld. Accordingly, noise included in the detection signal can be removed by the filtering portion so a weld on a work after rolling can be detected.
The technology in JP-A-61-151455 detects a weld by detecting a change in impedance from the eddy current. Therefore, when detecting a weld on a work that has been heat-treated, the crystal composition of the work has been made uniform, so the weld may be undetectable. That is, the detection accuracy may be reduced.
Also, JP-A-2005-283303 describes technology for detecting a flaw in a metal ring. In the technology described in JP-A-2005-283303, a driving pulley, a driven pulley, and a benchmark index detecting mechanism are used to detect a flaw in a metal ring. The metal ring is wound around the driving pulley and the driven pulley. The benchmark index detecting mechanism is arranged between the driving pulley and the driven pulley, and image-verifies a weld trace formed along the sheet width of the metal ring at the weld. The driving pulley is rotated to convey the work, and the position of the weld trace is detected by the benchmark index detecting mechanism. Also, flaw detection is performed by a mechanism that detects a flaw in a metal ring, and the detected position is identified as a relative position from the weld trace. The weld on the work is able to be detected using this kind of benchmark index detecting mechanism that detects a weld trace.
However, when a weld on a work is detected using the technology described in JP-A-2005-283303, the coloring and shape of the weld trace may change depending on the welding conditions such as the bead width and the like. That is, the weld trace may become difficult to see and thus may not be able to be detected. As a result, the accuracy with which a weld is detected may decrease. Also, although it is possible to reduce the rotation speed of the driving pulley to increase the detection accuracy, doing so would increase the time that it takes to detect the weld.
Also, a neck (an extremely small change) like a cutout toward the inside in the sheet width direction is formed at a weld on a work that has been rolled after welding. While it is possible to detect a weld on a work by detecting this kind of neck, the conveying speed of the work must be increased in order to detect the neck quickly, which means that an expensive sensor with extremely short measurement intervals must be used. That is, it is costly. On the other hand, if a sensor with long measurement intervals is used, the speed at which the neck is conveyed must be slowed so as to not skip over the neck. That is, it takes more time to detect the weld.